Phase shift heat control for welders



June 12, 1951 s. G. VIGARS PHASE SHIFT HEAT CONTROL FOR WELDERS 2Sheets-Sheet 1 Filed Feb. 9, 1950 lnventor B5 I I l W (Ittorneg June 12,1951 s. G. VIGARS 2,556,715

PHASE SHIFT HEAT CONTROL FOR WELDERS Filed Feb. 9, 1950 2 Sheets-Sheet 262777 60072904 v I J FIJI-770? 6a Bnventor Patented June 12, 1951 PHASESHIFT HEAT CONTROL FOR WELDERS Sterling G. Vigars, Royal Oak, Mich.,assignor to General Motors Corporation, Detroit, Mich, a

corporation of Delaware Application February 9, 1950, Serial No. 143,17

8 Claims. 1

This invention relates to welding control means andzmore specifically toadjustable control means for sequentially operating groups of weldingheads in sequence. In many installations it is necessary to fire aplurality of spot welders at one instant and immediately follow that bya second or third group to, in a relatively short time, secure togetherdesired parts. These parts may be of different thicknesses and difierentcontours at spaced positions and it, therefore, may be necessary toapply different total heats to the different groups of spot welds.

It is therefore an object of m invention to provide a control system forsequentially energizing different groups of electrodes for weldin and toseparately adjust the proportionate amount of heat available to theindividual groups.

It is a further object of my invention to provide sequential group weldcontrol means in which any one group may be adjusted to provide thedesired heat without in any way affecting any of the other groups.

With these and other objects in view which will become apparent as thespecification proceeds, my invention will be best understood byreference to the following specification and claims and theillustrations in the accompanying drawings, in which: 4

Figure 1 is a circuit diagram embodying a system including my invention.

Figure 2 is a group of curves of the voltages and currents appearing onthe control tubes.

Figure 3 is a similar group of voltage and current curves illustratingthe effect of varying the phase by the means disclosed.

Referring now more specifically to Figure 1, there is shown therein amain pair of power input lines 2 and 4 controlled by main switches 6 and8 respectively, switch 6 being connected by line H) to a pair ofnormally open contacts W1 and thence through line I2 to one side of theprimaries l4 and I6 of two welding transformers. It might be mentionedat this point that while two welding transformers are shown, an numbercan be used with this system, and two is merely illustrative. It isdesired to point out also that the relay coils are referred to byletters and that the contacts operated by each relay coil are likewisereferred to by the same letters as the coil and with a followingsub-number to differentiate the different contacts, but to identify themwith their control relay. To further assist in tieing the operatedcontacts back into its operating relay, we have shown in dotted arrowlines the direction of the control relay from the contacts. The secondmain switch contact 8 is connected through line l8 to a second normallyopen pair of contacts W2, and thence through line 20 to lines 22 and 24,extending itself to a mercury pool electrode 26 in ignitron, 28. Tapline 24 likewise extends from line 20 to the mercury pool electrode 30in ignitron 32 and tap line 22 extends from main line 20 to line 34.

A second set of control power input lines 36 and 38 are connected to thecontrol panel power and extend to two manually operated switches 40 and42, the movable terminal of switch 40 being connected through line 44 toone side of a plurality of control relay coils RI, Tl, R, R2 and T2.Line 36 is connected through tap line 46 to a pair of normall closedcontacts R1, which are operated by main relay R. The opposite side ofthis pair of contacts is connected through line 48 to a manuallyoperated switch 50 and thence through line 52 to one side of a controlrelay coil W. The opposite side of relay coil W is connected throughline 54 to a second manually controlled switch 56 and thence throughline 58 to one side of a second pair of normally closed contacts R2,likewise controlled by control relay R and then finally through line 60to the opposite control line 38. A relay coil 62 is connected betweenlines 48 and 58 and controls the hydraulic control pressure.

One side of control relay coil BI is connected through line 64 to oneside of a normally closed pair of contacts Tli, the opposite side ofwhich is connected through line 66 to tie line 68 extending betweenrelay TI and a selector switch 10. Selector switch 10 is connected alsoby line 12 with line 14, the latter extending between a control pressureswitch 16 and one side of a pair of normally open contacts T22. Pressureswitch 16 is also connected directly to manually controlled switch 42.One terminal of relay R. is connected through line 18 to stationarycontact of selector switch 82 and also to the other side of normallyopen contacts T22. A second stationary contact 84 on selector switch 82is connected through line 86 to stationary contact 88 of selector switchIll and also through tie line 90 with one side of normally open contactsT12. Relay R2 is connected through normally closed contacts T21 to arm82.

That portion of the system so far described initiates the cycle andlikewise proceeds to, in timed relation, sequentially provide energy forthe different groups controlled by the welding transformers, and isoutlined in dot and dash lines as will be noted.

The second section shown immediately below and also outlined in dot anddash lines may be referred to as the phase shift control portion of thesystem. This consists of the main control transformer primary TP, oneside of which is connected through tie line 92 to main line I2, theopposite side being connected through lines 3 3 and 22 to main line 20.It is, therefore, energized at all times when relay coil W is energizedto close its contacts W1 and W2. Transformer primary TP is center tappedand to the center is connected a windin TPA, the opposite end of whichis connected to one end of a Variable resistor 24 and also throughcondenser 96 to line 92. The adjustable tap 98 on resistor 94 isconnected through line I to adjustable tap I62 on a second variableresistor I04, and also to adjustable tap I06 on a third adjustableresistor I98. Resistance I04 is likewise connected to a pair of normallyopen contacts Rili operated by relay RI, the opposite side of which isconnected directly to line 34. In like manner resistor Hi8 is connectedto a pair of normally open contacts R21, also connected to line 34. By

, adjusting the position of adjustable taps I02 and I65, the phase ofthe control may be shifted to provide different amounts of heating, aswill appear in the following more detailed discussion.

The third dash and dot outlined section of I my control system containsthe thyratron controls which are commonly used with each group offollowing ignitron contactors, the latter, of course, being the actualfiring means. This section consists, therefore, of two controlthyratrons Hi3 and H2, each capable of controlling Opposite half cycles,two secondary transformer coils TS and T81, both inductively coupled tothe primary TP, and two secondary coils TSA and TSA1 inductively coupledto primary coil TPA.

The connections of these various parts will now be more described indetail.

One end of transformer coil TS is connected through line I I4 to aresistance I IS, in turn connected to control grid H8 of tube H2. Acondenser IZU is directly connected across resistance H6. The oppositeend of transformer coil TS is connected directly to one terminal of thesecondary coil TSA and that in turn is connected through line I22 to theplate I24 of tube Hi! and to the cathode iZfi of the tube H2. The sametype of connections exist on the opposite side for controlling the otherhalf cycle in that transformer T81 is connected directly throughresistor I28 to control grid I30 of tube H0 and has condenser I32connected directly across said resistor. Transformer secondary T81 isalso connected to transformer secondary TSAi and thence through linesI34 and I36 to plate I38 of tube H2, and also to the cathode I46 of tubeH0. These tubes will alternately conduct on opposite half cycles atpredetermined positions in their energizable time, depending upon thecontrol set forth above. When these conduct, they cause the ignitronscontrolled thereby at that particular instant to fire and weldin currentthrough the transformers results.

The last and final section to be described is that enclosed in dot anddash lines at the bottom of Figure 1, and this consists generally of apair of ignitron tubes and a weldin transformer for each group of spotwelders which it is desired to control, and as mentioned previously weare here concerned illustratively with only two, although the numbercould be as large as desired. In this instance control line I42 extendsfrom cathode I26 of tube H2 down to a pair of normally open contacts BIZand thence through a normally closed thermo switch I44 and a fuse ILIISto one side of a half wave rectifier I48 and also to the opposite sideof a half wave rectifier IEIE, the direction of current flow beingindicated. The opposite side of rectifier M8 is connected to theigniting electrode I52 of the tube 32 and the opposite side of therectifier [Eli is connected through line I54 to the mercury electrode 3dof the tube 32 and also to the spaced or plate electrode I56 of a secondignitron tube I58. In like manner the spaced plate electrode Hit of thetube 32 is connected through line I62 to the mercury electrode $4 of thetube I58. Line Hi l, which proceeds downwardly from thyratron lid, isconnected through a normally open pair of contacts Biz and thence to twohalf wave rectifiers I66 and IE8 connected respectively to the ignitingelectrode III} and the mercury electrode I64 respectively. Line I12interconnects the mercury electrode of tube I58 with one terminal of thewelding transformer primary I4, which has connected thereacross a surgeresistance I'M. Thus the two thyratrons H2 and III} alternate-- 1ycontrol the firing of the ignitrons 32 and I58 to provide alternatelyhalf cycles of welding power to transformer I4.

Afterthe welding by transformer I4 is accomplished, ignitrons 32 and I58are switched out of the circuit and are replaced by ignitrons 28 and H6.Line I42 also extends down to and is connected to a pair of normallyopen contacts R22 and thence through a thermo overload switch IlIl andfuse ISO to two half wave rectifiers I82 and I85, rectifier I82 beingconnected to igniting electrode I86 of tube 28. Plate I88 of tube 28 isconnected through line I913 with a mercury electrode I92 of tube I16 andlikewise to one side of the transformer primary I 6 of the secondwelding transformer. Half wave rectifier I84 is also connected to themercury electrode 26 of tube 28 and through line I94 to the spacedelectrode or plate I96 of tube IIB. Line I34, extending from thyratronIII is also connected to one side of a pair of normally open contactsR23 which are in turn connected to two rectifiers I98 and 26B, rectifierI98 being connected to igniting electrode 2E2 of tube H6.

The operation of this system, as indicated above, provides a series ofsequential groups of welds; that is, several spot welds will beperformed by the firing of the tubes 32 and I58 to energize transformerprimary I4 and the amount of heat provided in each weld will becontrolled by the settings on resistors 94 and H34 in series. Then nextin sequence, another plurality of spot welds will be performed by theenergization of tubes 28 and I I6 and the amount of heat developed inthis plurality of welds will be determined by the adjustable settings onresistors 94 and IE8 in series.

The heat control is provided basically by the resistive-reactive networkenclosed in the dash and dotted outline at the upper center of thesystem. The secondaries of the peaking transformer TS and T31 areconnected to the grid circuit of the associated heat control thyratronsso that the voltage of these secondaries will lag the plate voltageapplied to these tubes. The amount of this lag is determined by theamount of resistance in the phase shift control circuit includingprimaries TP and TPA and indicated as variable resistances 94, I04, andI03, With zero resistance or with each of these rheostats moved to aposition to cut out the resistance involved, the la is zero degrees andwith the resistance portion of the circuit open or infinite resistancethe lag is 180.

The resistance portion of this phase shift circuit consists of whatmight be termed a heat control resistor for each of the groups ofwelders which are to be fired. Resistor I04 acts as the heat controlresistor for the first group of ignitrons 32 and I58. In like mannerresistor I08 acts as the heat control resistor for the second band ofignitrons 28 and I16. Associated with each of the heat control resistorswhen it is in circuit is what might be termed a power factor adjustmentresistor 94 which is common to all of the circuits and is set initially.For example, with all the resistance of resistor I04 cut out, the powerfactor adjustment resistor 94 is adjusted to compensate for the normalpower factor of the load. This brings the peaking voltage in phase withthe load current. This peaking voltage overcomes the negative biassupplied by TSA or TSA1, as the case may be, and causes the thyratrontube to fire at the beginning of the cycle. When this occurs the resultis 105% heat or all that can be obtained from a single cycle and is thecalibration of any indicator on resistor I04 or I08 when set for nominalzero resistance.

Increasing the resistance of either M4 or H18 in the circuit willdecrease the amount of heat obtained per cycle, since it causes thepeaking voltage to lag in an amount dependent upon its setting. ResistorI04, or rather tap I02 thereon, can be adjusted to vary the percent ofheat or current over practically a full range. Indicating means on theadjustment of resistor I64 can be calibrated as a measure of percentageheat derived. This can be further described by reference to the showingsof Figure 2 and Figure 3 of the drawings in which various voltage andcurrent curves are shown.

Referring specifically to Figure 2, there is shown therein a curvelabeled E which is the normal voltage applied to one of the thyratronsH2 or II!) from the main line. A second curve of smaller heightdesignated IL, or load current, discloses the phase difference in thevoltage applied to the thyratron and the current at the load when fullheat is applied. Eco indicates the voltage on the grid bias and Es, thepeaking voltage. The dotted line indicates the critical grid voltagecurve. A study of these curves will dicate their time phase differencesand it will be seen by shifting the peak voltage Es along the time baseby a variation in the phase control resistance that the triggering ofthe thyratron may be varied in time relation, that is, later or earlierin the main voltage cycle, to cause more or less total current to fiowper half cycle.

This is perhaps better illustrated by further reference to Figure 3 inwhich there is illustrated the movement of the peaking voltage along thetime base. E in this instance still indicates the voltage from the lineapplied to the thyratron plate and IL is now shown in dotted lines,since we do not obtain the full current. The peaking voltage Es has beenmoved along the time axis and now triggers the tube at a later instantin the cycle and IL indicates the total current at reduced heat. Thedistance between the starting instant of the voltage curve Ep and thestarting instant of the dotted line indicating IL at full heat isdetermined by the setting on resistor 94,

which has previously been referred to as the power factor resistor, andthis is a constant distance or delay being preset for given loadconditions. The second horizontal distance, that is, between thebeginning of the dotted line curve IL at full heat and the beginning ofthe curve II. at reduced heat, is controlled by the setting on resistorI04 or [08 as the case may be, and is adjustable, depending upon thedesires of the operator.

In the operation of this system, therefore, the operator would firstadjust and set adjustable tap 98 on resistance at to compensate for thepower factor of the load. He then would adjust the various taps I52 onresistor I04, and tap I05 on resistor I68, and any further adjustableresistors if more than two banks or welders were to be fired for theheat setting which was desired on each bank. With the system then readyto be operated, main switches 3, 3 and 40, 42 are closed. At this timerelay W is energized through an obvious circuit to close contactors W1and W2. The pressure switch I6 will then be closed by an increase inpressure on the welding machine, and when this closes, timer relay TIstarts to time out, and relay R! is energized, since TI and RI are inparallel circuit relation across the main power lines 36 and 33 at thispoint. When RI is energized, it closes its contacts Rh, Biz, and Biz.The closure of contacts Rh completes the energizing circuit through thephase shift control circuit as follows: from main line 20 through line22, line 34, transformer primary TP and line $2 to opposite main lineI2, and at the same time a parallel circuit from line 22 through line 35, contacts Rh, resistor I64, tap Hi2, line I69, tap 58, resistor Q4,condenser 36 and line 92. Biasing transformer primary winding TPA is, ofcourse, included in this circuit.

At this time power is also supplied in alternate half cycles to thecathodes and plates of the heat control thyratrons HE and H2, but theywill not fire until the bias voltage applied to the control gridspermits the same. The energizing circuits for the thyratrons onalternate half cycles when the plate becomes positive are, of course,practically identical and only one of these energizing circuits will bespecifically traced, it being assumed that the other will be cleartherefrom. Full line voltage appears across the plate and cathode ofthyratron lll through the following circuit: supply line 25, line 24,rectifier I50, fuse Mt, normally closed thermally actuated safetycontacts M l, contacts R52, when closed, as just described, line M2,line E22 to plate I24, then from the cathode I45 through line 234,contacts Rlx, which have just been closed, rectifier I66, ignitingelectrode its of ignitron 558, line Iil, primary winding i l of thewelding transformer to main line I2.

However, since the thyratron H8 is biased to cut off, no current canflow until a sufiicient voltage is applied to the biasing grid This isaccomplished by the voltages supplied by the transformer secondariesTSA1 and TS1, which apply said voltage through resistor I23 to thecontrol grid I30 in such phased relation as indicated by the settingE532 on resistor ltd. When this peaking voltage Es is applied to thegrid its thyratron Ilil conducts, which completes the energizing circuitthrough the ignitron as just traced, and welding current is supplied tothe transformer primary I4, whose value from maxi mum to minimum isdetermined by the setting I92. In the other half cycle tube H2 triggersignitron' 32 in' exactly the same manner as tube Hi! triggers tube [58and exactly the same amount of heat or current is supplied to thetransformer primary 14' in the next half cycle and it is determined aswell by the setting in on the resistor I64. This action continues aslong as relay RI remains energized, which is, of course, for apredetermined number of cycles, which time is determined by timer relayTI, and when that has timed out, it is energized, being the type ofrelay which is time delay actuated to close and it then opens itscontacts Til and relay RI is deenergized.

When this occurs, contacts Rh are opened to deenergize phase controlresistor IE4, contacts Rlz are opened to open the circuit to ignitron32, and relay contacts Rls are likewise opened to open the circuit toignitron i533. Therefore, all of the first set of ignitrons and thefirst welding transformer are now excluded from the system. When timerrelay TI is energized to deenergize relay RI, it also completes orcloses a circuit for the energization of timer T2 by closing normallyopened contacts Tl2. Upon the energization of timer T2, relay R2,likewise in parallel relationship therewith, will be energized throughnormally closed contacts T21 which do not pick up until T2 times out.With the energization of relay R2, switches R21, R22, and R23 areclosed. These switches complete circuits to phase shift resistor H38,ignitron 28 and ignitron lit in exactly the same manner as relay R5 didin the first instance, and as soon as this occurs line voltage is againapplied. to thyratrons Hi and I [2, which now control the firing periodsof ignitrons 28 and H6 and the energized cycles of welding transformerHi. It is not believed necessary to specifically trace circuits in thisregard, as they are similar to. those of'ignitrons 32 and IE8. Whentimer T2 has now timed out, it will open its contacts T21, deenergizingrelay R2' and in turn deenergizing the control system for weldingtransformer I6. It will be obvious. that as many different controlcircuits may be supplied as banks of transformers desired, and when thelast timer has timed out, it will complete a circuit through relay R byclosing its contacts such as T22, the energization of relay R openingthe hydraulic solenoid valve 62 and when pressure is thus removed thepressure switch 76 drops out and the control system is deenergized.

I claim:

1. In a welder control system for energizing a plurality of weldingtransformers in sequence; electronic means connected to the primaries.of each of the transformers to control the conductive periods thereof, acommon electronic control means, a first switching means connecting saidcommon electronic means with any one of the first named electronicmeans, a phase shifting network connected to the common electronicmeans, said phase shifting network including a plurality of parallelpaths ofsimilar components of adjustable value, said plurality of pathsbeing equal to the number of transformers to be controlled, a secondswitching means in each path, a source of power, and sequentiallyactuated timer relay means connected to the source and to both switchingmeans to simultaneously switch the parallel paths and the first namedelectronic means for a given transformer.

2. In a welder control system for energizing a plurality of weldingtransformers in sequence, electronic means connected to the primaries ofeach of the transformers tocontrol the conduc- Cir tive periods thereof,a common electronic" means of the grid bias type, a first switchingmeans connecting said coimnon electronic means to any one of the firstnamed electronic means, a resistance-reactance network inductivelycoupled to the biasing means of the common electronic means, saidnetwork including a plurality of parallel paths and adjustableresistances in each path, the number of paths being equal to the numberof transformers to be actuated, a second switching: means in' each path,a source of power, a plurality of time controlled sequentially operatedrelays connected to the source of power and relay means controlled bythe time controlled relays and actuating. both the first and secondswitching means to sequentially energize one path in the network and oneof the first named electronic means at a' time to control the heatingeffect of a given transformer.

3. In a welder control system for energizing a plurality of weldingtransformers in sequence, electron tube means connected to the primaryof each transformer to determine its inductive periods, a secondelectron tube means, biasing means for said second electron tube means,a resistance-reactance network inductively coupled to said biasingmeans, a plurality of parallel paths each having a variable resistortherein in said network to control the phase of the biasing voltage,switching means for connecting the second and sequentially the firstelectron tube means and in the parallel paths of the network to includeone path for each first electron tube so that one transformer isenergized at a time in order and its heating effect is determined by thesetting on the variable resistor then in circuit.

4. In a welding control system, a plurality of welding transformerswhich it is desired to energize sequentially, electron tube controlmeans connected to each transformer, common multi-electrode tube means,switching means for connecting said common tube means to each of thefirst named tube control means, a source of power connected to theswitching means so that when the switching means are closed and thefirst named electron tube control means is fired by a control pulse fromthe common multi-element tube means, the associated welding transformerwill be energized, biasing means for the multi-electrode tube means, anda resistive-reactive network including parallel adjustable resistancepaths inductively coupled to the biasing means and to the power sourcetocontrol the firing pulse initiation.

5. In a welding control system, a plurality of welding transformerswhich it is desired to energize sequentially, electron tube controlmeans connected to each transformer, common multielectrode tube means,switching means for connecting said common tube means to each of thefirst named tube control means, a source of power connected to theswitching means so that when the switching means are closed and thefirst named electron tube control means is fired by a control pulse fromthe common multi-element tube means, the associated welding transformerwill be energized, biasing means for the multielectrodev t'ube means,said biasing means including a plurality of phased inductive windings inseries connected to one of the elements, a resistive-reactive networkincluding a plurality of parallel adjustable resistance paths connectedto inductive means mounted in juxtaposition to the inductive means ofthe biasing circuit, switching means in the parallel paths so that onlyone may be used at a time and means to connect the network to the powersource so that voltage flowing therein may be dephased and applied tothe biasing means to control energization of the multi-element tubemeans.

6. In a welding control system, a plurality of welding transformerswhich it is desired to energize sequentially, electron tube controlmeans connected to each transformer, common multielectrode tube means,switching means for connecting said common tube means to each of thefirst named tube control means, a source of power connected to theswitching means so that when the switching means are closed and thefirst named electron tube control means is fired by a control pulse fromthe common multi-element tube means, the associated welding transformerwill be energized, biasing means for the multielectrode tube means, saidbiasing means including a plurality of phased inductive windings inseries connected to one of the elements, a resistive-reactive networkincluding inductive means coupled to said windings in the biasingcircuit, a common adjustable resistance connected to said inductivemeans and a plurality of adjustable resistors connected to the sourceand to the common resistance, the common resistance,adjustmentcompensating for the load and each of the parallel resistors adjustingthe phase of the trigger pulse applied to the biasing circuit, switchingmeans in the parallel resistance circuits so that only one variableresistance at a time will be in circuit and common relay means toactuate both the first and second named switching means.

7. In a control system for energizing a plurality of transformers insequence for energization for differing cyclic intervals to obtaindifferent amounts of energization from each, a multi-element electroniccontrol means, a source of power, a plurality of adjustable phase shiftnetworks, a first switching means to connect each phase shift networkseparately between the control elements of the electronic control meansand the source of power, a second switching means to connect theelectronic control means separately to each transformer, a common timedsequence switch actuating means to operate one element of the firstswitching means and one of the second switching means simultaneously asa pair, and the pairs in sequence to provide each transformer with oneof the phase shifting networks to control the energization thereof.

8. In a welder control system for energizing a plurality of weldingtransformers in sequence for differing cyclic intervals to obtaindifferent amounts of heating from each, a source of power, amulti-electrode electronic control means, a plurality of adjustablephase shift networks connected to said source, switching means toconnect each separately to the control electrodes of the electroniccontrol means, a second switching means to connect the electroniccontrol means to each transformer, and a common timed sequence switchactuating means to operate one element of the first switching means andone of the second simultaneously and the pairs in sequence to provideeach transformer with one of the adjustable phase shifting networks tocontrol the energization thereof.

STERLING G. VIGARS.

No references cited.

